The present invention relates to a NOx removal system to be used in boilers for reducing NOx.
In recent years, there has been a desire for further NOx reduction also in boilers. One of the measures therefor is a method that with a NOx removal system provided in the boiler, ammonia as a reductant is supplied to discharge gas, thereby reducing the NOx. While this ammonia is generated by heating urea water, piping from the ammonia generating means to ammonia jet nozzles is provided with heat retention means such as heat insulating material or warming means such as electric heater. This is because ammonia, if decreased in temperature during its flow through the piping, would cause intermediate products to be generated or the piping to be clogged due to crystallization. Such disadvantages tend to occur particularly with the piping longer.